What is an outlier in a data set?

An outlier in a data set is defined as a value that is significantly higher or lower than the other values in that set. This extreme deviation from the rest of the data may indicate variability in the measurement or may suggest a mistake in the data collection process. Outliers can have a substantial impact on statistical analyses, as they can skew results, affect averages, and distort patterns observed in the data.

Identifying outliers is important in data analysis because it helps in understanding the overall distribution and can lead to more accurate modeling and conclusions. For example, in a set of test scores where most students score between 70 and 90, a score of 30 would be identified as an outlier because it is noticeably lower than the majority.

The other options describe concepts that do not align with the definition of an outlier. A value that occurs most frequently pertains to the mode, a value exactly in the middle refers to the median, and a negative value does not necessarily convey the same information about its relationship to other values in the set.